1. Field of the Invention
The invention relates to an arrangement for scattering electrons, preferably in electron accelerators with variable acceleration energy, the arrangement comprising two mutually spaced scattering foils whereby the first scattering foil in the beam direction has a constant thickness and the second scattering foil has a thickness which decreases from the center to its margins.
2. Description of the Prior Art
In the case of electron accelerators which must expose several cubic decimeters of volume with a constant intensity, it is known in the art to use two different foils arranged at a distance from one another for scattering the electrons (see German Letters Pat. No. 9 599 37.).
According to the prior art, the first scattering foil in the beam direction serves for scattering the electron beam. The second scattering foil is to compensate or equalize the intensity of the scattered electron beam. Since the thickness of the first scattering foil may not be selected very large due to energy losses, and since the resulting homogeneity of the intensity distribution obtained in the beam cone scattered by the first foil is insufficient, the second scattering foil must have a thickness which decreases from its center towards its margin in order to have a greater reduction of the intensity in the center range than in the marginal range of the beam cone.
However, the scattering properties of such an arrangement are also dependent, in addition to the properties of the two scattering foils, on the mutual tuning of the two scattering foils; the centering of the second scattering foil with respect to the center beam; and the energy of the electrons which are to be scattered. Thus, a different arrangement is required for each acceleration energy. This is considered to be a large drawback since scattering foils, particularly the second one, are cumbersome to produce and thus expensive. Their exact centering with respect to the electron beam cone must, in addition, be very precise.